The present invention relates genera to integrated circuit (PC) packaging and specifically to IC packaging which provides a hermetic seal and reduces dose enhancement from secondary electrons.
In the design of IC packaging that will be used in radiation environments, attention must be given to designing the package so as to protect the circuits from damage due to radiation. Spacecraft or satellites traveling in typical earth orbits are exposed to a natural space radiation environment including gamma rays, x-rays and other high energy particles. Electrons and x-rays are the principal contributors to total dose radiation problems within a spacecraft or satellite. The type of interactions that occur between photons and the atoms in a bombarded or exposed material depends on the atomic number of the target material. X-rays become absorbed by a targeted atom and the atom emits an electron. For atoms having a high atomic number it is easier to liberate an electron than it is for atoms having a low atomic number.
The lid or cover of an IC package has an underside which is typically located near and facing the active region of the IC chip. Package lids are typically made of a nickel/iron alloy, such as kovar that has been nickel and gold plated. During package assembly the lid is typically brazed to the package with a gold/tin eutectic solder. Unfortunately the gold plated surface of the underside of the lid is facing the integrated circuit and will be a generator for electrons when the package is exposed to x-rays and other radiation. The active region of the chip is located near the top surface of the chip, and it is the dose in the active region which affects IC performance. The gold surface of the underside of the lid when bombarded with high energy particles liberates electrons to the chip surface. This electron showering of the integrated circuit can affect performance.
Thus a need exists for a package that will minimize total dose enhancement from secondary electrons.
The present invention solves these and other needs by providing an integrated circuit package for use in radiation environments which includes a base for receiving a die and a peripheral surface. A lid has a peripheral seal area that rests on the peripheral surface and an inner surface that faces the die, the inner surface has a cladding of a metal with a low atomic number to minimize electron emission due to absorbed radiation.